The disclosure concerns a method and a system to process color print images for digital printing. Relative to offset printing, digital printing is distinguished by a high flexibility since, in digital printing, it is possible to print different print images in succession. In contrast to this, in offset printing a defined print image is repeatedly printed with a predetermined print run.
It is known to review (and, if applicable, to correct) digital print data before the printing process with a preflight software. In particular, a check is hereby made as to whether the print data are correctly formatted and correspond to the corresponding data type for the printing process. In particular, a check is made as to whether all data can be accessed; whether all fonts are activated; whether the color spaces are correctly assigned; whether the lines/contours are vectorized or pixelated; whether the print data possess the required resolution; whether the correct spot colors are included in the document; and whether the trapping is correct. This preflight method is used similarly both for offset printing and for digital printing.
The processing of print images in offset printing differs from that in digital printing in that the print images are deconstructed into color separations in offset printing. The individual color separations represent greyscale bitmap images. Offset printing plates for the offset printing are generated using the color separations by means of an exposer. The offset printing plates serve to transfer a defined colorant onto a recording medium.
In digital printing, as a matter of principle the translation of the color values of the print data into the colors of the print groups of the printing apparatus takes place completely differently. The print data can include characteristic color curves for the individual color objects. At the print server associated with the digital printing apparatus, or in the control device of the digital printing apparatus, these are then compared with the characteristic curves of the print colors of the printing apparatus and converted accordingly. Alternatively, the print data are represented with standardized color spaces (for example CMYK, RGB, LAB), and rule-based color corrections are implemented in the preflight method (at the print server or in the control device of the printing apparatus) in order to convert the standardized colors into the print colors of the printing apparatus. The deconstruction of the print data into the individual print colors only takes place immediately before the rastering or in the rastering of the print data. The rastered print data are then relayed directly to the respective print heads of the digital printing apparatus.
Digital printing is more flexible than offset printing. However, the quality of offset printing is normally better than that of digital printing. One of the reasons for this is that the print colors are normally more precisely adjustable in offset printing than in digital printing.